Major depressive disorder (MDD) is common in adolescents and results in significant morbidity and mortality. Adolescent suicides are the third leading cause of death for this age group typically accounted for by depression. There is a high rate of only partial response to the most commonly used group of antidepressants (SSRIs) and increased controversy regarding their use for this age group. These findings coupled with recent decreased SSRI prescription rates with concomitant increases in suicide, constitutes an important public health problem. And for adolescents, there is a lack of available safe, effective, and easy to use nonmedication treatment alternatives with controlled data. Aerobic exercise can provide a safe, effective, minimal side effect treatment intervention that may be more acceptable to patients and potentially cost effective. This study proposes to 1) develop a depressed adolescent exercise treatment manual based on the recent successful UT Southwestern depressed adult exercise study, 2) evaluate the feasibility of using a standardized aerobic exercise regime to treat nonmedicated clinically depressed adolescents based on adherence and completion rates, 3) establish effect sizes for the primary outcome (the CDRS-R and Actical [energy expenditure data] as well as selected secondary outcomes; [e.g., QIDS-A17, attitudes], and 4) determine whether exercise versus stretching activity leads to clinically meaningful reduction in depressive symptoms and/ or improved psychosocial functioning. The proposed study will consist of providing AEROBIC EXERCISE or PLACEBO STRETCH to mild to moderately depressed nonmedicated adolescents recruited from community physicians, advertisements, and UT Southwestern outpatient clinics. Sixty clinically depressed adolescents of both genders between the ages of 12 -17 years who meet criteria for DSM-IV major depression (CDRS-R = 36 =70 and CDI-S = 4) will be randomized to an aerobic dose exercise or a placebo stretch condition for 12 weeks. Based on current recruitment, and rates achieved in the UT Southwestern adult depression exercise study at the Cooper Institute in Dallas, we anticipate at least 60 will be randomized to the 12 weeks exploratory feasibility trial in the allotted time. Comprehensive state of the art processes for monitoring adherence with web-based tools and Actical 24/7 monitoring are coupled with motivational techniques for depressed youth to assure a successful completion rate. [unreadable] [unreadable] [unreadable]